The invention relates to a blind fastener, that is, one which can be installed by access to one side only of a workpiece. More particularly the invention relates to a blind fastener of the type comprising a pin, a sleeve, and an abutment member. In use of the fastener in a workpiece comprising two or more members to be secured together, the pin and sleeve are inserted through an aperture in the workpiece so that their remote end portions protrude beyond the remote or blind face of the workpiece. The application of axial compression to the sleeve by means of a pulling force on the pin with respect to the sleeve causes the protruding end portion of the sleeve to deform into a blind head which contacts the blind face of the workpiece. The workpiece is then compressed between the blind head and the abutment member and the abutment member is then secured to the pin, to secure the workpiece members together in the compressed condition. The creation and retention of this compression is important for the strength of the resulting joint.
There are alternative possible ways of providing the necessary mechanical engagement between the various component members of the fastener. The remote end of the pin may have a radially protruding head which contacts the end of the sleeve to apply compressive force to it, or the remote end of the pin may be in threaded engagement with the sleeve. The abutment member may be permanently securable to the near end portion of the pin by means of swaging, or may be removably secured by means of a threaded connection.
The application of an axial compressive force to the sleeve in order to form the blind head obviously requires that the near end of the sleeve is supported, in order to put it into axial compression. However, at a later stage in the installation process, when the workpiece is compressed between the abutment member and the blind head, it is important that none of this compressive force is supported by the sleeve, otherwise the compression applied to the workpiece would be reduced. These two design requirements are not straightforward to combine. At the same time it is also desirable that the fastener has as large a grip range as possible, that is to say that identical fasteners will successfully work in workpieces of different total thicknesses. This also imposes design constraints on the fastener. One way which has been used is to provide a shearable member between the abutment member and the near end of the sleeve, which initially supports sufficient axial compression on the sleeve to form the blind head, but fractures when the load applied between the abutment member and the sleeve increases. One such fastener is described in detail in EP 0705986 A and equivalent U.S. Pat. No. 5,603,592. However it is apparent from those documents that the construction of the fastener is complicated, involving a multiplicity of parts to be manufactured and assembled together. For instance, the sleeve is in two parts, and there are separate abutment, abutment securing, and shearable members. This increases the cost of manufacturing the fastener. Also, the head assembly of the fastener is of necessity deep, in order to accommodate both a useful grip range and the closing of any gap which may exist initially between the workpiece members.
The present invention aims to allow the provision of a fastener of simpler and smaller construction.
The invention provides, in one of its aspects, a blind fastener as set out in claim 1 of the accompanying claims. Further features of the invention are set out in claims 2 through 6. The invention includes a method of forming a riveted joint, as set out in claims 7 and 8. The invention also includes a riveted joint as set out in claim 9.